Apparatus for static pulse rejection



Oct. 6, 1953 M M, NEWMN 2,654,835

APPARATUS FOR STATIC PULSE! REJECTION Filed Jan. 30, 1950 FIGURE l.

. so FIG. 7 |80 f Patented Oct. 6, 1953 APPARATUS FOR STATIC PULSE REJECTION Morris M. Newman, St. Paul, Minn., asslgnorto Lightning & Transients Research Institute, Inc., Minneapolis, Minn., a corporation of Minnesota Application January 30, 1950, Serial No. 141,317

(Cl. Z50-20) 7 Claims. 1

My invention relates to apparatus for the elimi-J nation of the effects on radio receivers and navigational apparatus of static pulses, such as corona pulses under precipitation static conditions, pulses radiated from lightning discharges and pulses from sparking electric equipment, and has for an object to provide an apparatus whereby the static pulses are blanked out before they reach the receiver and set the receiver circuits into shock excitation. p

Another object of the invention resides in providing an apparatus in which the length of the static pulse is effectively shortened to reduce the time of blanking and the corresponding period of signal loss.

A still further object of the invention resides in providing an apparatus in which the desired results are obtained by the use of phased transmission lines to shorten the static pulses.

An object of the invention resides in utilizing transmission lines which are terminated in their characteristic impedances at their input ends and are short circuited at their outer ends and which have an electrical length approximately equal to one quarter of the desired signal carrier wave lengths.

Another object of the invention resides in providing a switching stage in which the receiver is effectively disconnected during the shortened period of the static pulse.

A still further object of the invention resides in providing a switching stage which is balanced to eliminate the introduction of noise into the receiver due to the inherent action of the switching device.

Another object of the invention resides in providing an apparatus in which a control channel for the most part separate from the signal chan-` nel leading up to the receiver is employed in which the static pulse is detected and modied.

An object of the invention resides in providing an apparatus in which the static pulse is iirst shortened in the signal channel, then lengthened a finite amount in the control channel to nally provide a blanking impulse for operating the switching stage.

Another object of the invention resides in providing an apparatus in which the shortened static pulse is reflected back upon itself a certain number of times to form a plurality of formed pulses.

An object of the invention resides in utilizing a cancelling transmission line of denite length to limit the number of formed pulse reflections and to prevent carrier signal resonance of the signal in the reflecting line.

An object of the invention resides in forming from the formed pulses a blanking pulse by inversion and full wa-ve rectification of the formed pulses.

A still further object of the invention resides in providing an apparatus in which the blanking pulse is used to trigger a pulse generator to secure a shaped blanking pulse of definite wave form regardless of the form of the original static pulse.

An object of the invention resides inproviding an apparatus in which the signal modified by the inherent action of the switching stage.

shortened pulse is delayed while the pulse is detected and shaped to blank out the pulse from the signal during an interval in which the delayed shortened pulse is arriving at the switching stage.

Another object of the invention resides in providing an apparatus in which a sequence of shortening lines, are employed to provide a short pulse from a variety of wave forms and to cancel pulse residue due to attenuation in the lines.

Other objects of the invention reside in the novel combination and arangement of parts and the circuits therefor hereinafter illustrated and/or described.

The invention herein disclosed comprises an antenna coupling stage which terminates the antenna in its characteristic impedance and which feeds a static pulse shortening transmission line which is terminated at its input end in its characteristic impedance and short circuited at its outer end and which is of an electrical length substantially equal to a quarter wave length of the desired mean signal wavelength Within the Signal band pass. This transmission line is coupled by a coupling circuit to a cancellation transmission line. This transmission line is terminated at its input end in its characteristic impedance and is short circuited at its outer end. This line is of a length, when chosen for optimum operation equal to an even number of times the length of the first shortening line. A tap is taken on this line to divide the same into two parts, one constituting a delay line for the signal carrier and the other a second shortening line. The signal is picked up at the 'tap and directed through a switching stage to the receiver. This switching stage utilizes a thermionic tube which is balanced by another thermionic tube, both feeding into a push pull transformer to eliminate the introduction of noise into the receiver due to the The cancellation line is connected at its input end by means of a coupling stage to a reiiecting transmission line which is of the same electrical length as that of the iirst shortening line, This line is constant magnitude or in its other position to' operate a pulse forming stage whichin .turnppf erates the switching stage for sporadic pulses l of This latter pulse widely varying amplitudes. forming stage includes a limiter and slicer is connected across the rectiiier and which feeds an amplifier. The output of )the amplier'is connected lto a pulse generator which in turn is adapted to be connected to the Vswitcliinglstage.

In the drawings:

Fig. 1 is a wiring diagram of an apparatus for static pulse rejection illustrating an embodiment ,of the invention.

Fig. 2 is an oscillogram .of the carrier vwaveon which is superimposed -a static puise as existing at the antenna.

Fig. 3 is a View similar .to Fig. 2 showing the wave after the same has passed through the rst shortening line.

Fig. .4 is a view similar to Fig. 3 showing the Wave as it exists at the Ysecond shortening line and at the input to the switching stage.

Fig. 5 is a view similar to Fig. 4 showing the wave after the same has been reflected by the cancellation line.

Fig. 6 is a View similar to Fig. 5 showing the wave alf-ter it has been reflected yby the reflecting line.

Fig. 7 is a view similar to'Fg. 6 of the wave afterthe same has passed through the inverter and rectifier.

Fig, 8 is a View similar to Fig. 'l showing the wave after it has been limited and sliced by the the limiter and slicer.

Fig. 9 is a View similar to Fig. 8 showing the wave aiter it has passed through the pulse forming stage.

Fig. 10 is an oscillogram of initted to the receiver.

My invention is connected between the antenna endreeeiver end for the purpose of .illustration en antenne indicated et l lhas been shown.. This antenna is connected et its output end to a coupling stage.Y lil- This coupling .stage in.- chides e resistor l? which is. connected to the output end of @ne antenna and which is grounded. The said coupling siege further includes e thermionic tube I 3 vhere illustrated as a pentode which has a plate I4, a suppressor grid I5, a screen grid I6, a control grid I1 and a cathode I8. The control grid Iis connected by means of a conductor I9 with the antenna I0 and resistor I2. The suppressor grid lV is connected to the cath ode I8 which in turn is connected through a cathode resistor 2 0 Icy-passed by condenser 2,3 to ground. The plate I4 is connected through a conductor 2l through a transfer condenserV 22 t0 e. first shortening transmission line 23. A termineting resistor ,2.4,v is Connected through e. oonductor 25 to the conductor 2| while the said resistor and the screen grid I6 are connected to a suitable source of plate current. The transmission line 23 as illustrated consists of a coaxial cable which may be of a high impedance spiral type and consists of an inner conductor 26 and an outer conductor Zi The eonduetors 2t end. 21 are shorted at the outer ends of the line and the wave transgrounded. The transmission line 23 is of an electrical length approximately equal to onefourth of the wave length of the mean wave length of the band to be transmitted. It will be readily comprehended that the length of this line, may `b e yaried within jlimits to move the optimum response point .to Vcorrespond with any vdesired signal band.

A The transmission line 23 is also connected by lmeans offa .conductor 29 to a coupling stage 33. coupling 'stage is similar to the coupling s tage II and the description thereof will not be iflepeated. This stage includes a pentode 3l and A resisto121i `."SZandY 3-3. These resistors are connected to the said pentode in the same manner as the resistor I2 and the resistor 24 of the stage fheresistors 1.4 and 32 have a combined value substantially equal to the characteristic impedance of the transmissionv line 23. The plate of the pentode 3l is connected by means of -a conductor 34 through a transfer condenser 35 to a cancellation transmission line 3'1. The cancellation line 31 is of the same type as the line 23 and has `an inner conductor 38 and an outer conductor 39. The -two conductors 38 and 33 are shorted at the outer end of the line 31 and are grounded. The length of the line .31 is equal to a-n even numbered multiple of the length of the shortening line. kIn the particular line shown the multiple is six.

|The cancellation transmission line 31 is `connected by means of a conductor 4S -to another coupling stage 42. This coupling stage is similar to the coupling stage I I and comprises a pentode 43 and a resistor 44. The said pentode and resistor are connected in the same manner as the pentode I3 and resistor I2 are connected in the stage Il. The resistor 44 and the resistor v33 have a combined resistance equal to the characteristic impedance or the cancellation transmission line 31. The plate of the tube 43 is connected by means of a conductor 45 to a refleeting line 46. This reflecting line is of the seme type and .length as the rst shortening line 23; This transmission `line has an inner conductor 41 and an outer .conductor 48, which are snorted at the outer end of the line. '1 -he conductor 41 of line ,46 is directly connected to the conductor 45 which in turn is connected to a .cQlldilQtor 4S. The outer conductor 48 is bypassed through a'condenser 5c to ground and is k.connected by means of .a .Conductor .5| toa source .of plete supply current.

The reflecting line 46 is connected by means o f conductor 49 toY an inverter 52. This inverter consists of a twin triode 5.3 Which has plates 5.4. and 55, control grids .5B and 51 .and .Cathodes 58 and 5 9. The cathodes 58 and 59 are connected together and to a cathode resistor 6 0 te ground which is ley-passed by a condenser |83. The grid 5 6 is connected to a resistor 5I which is grounded.V The said grid and resistor are further eonneeted'to e Condenser e2 which is connectedfto the conductor 43. vThe grid 51 is similarly connected to a grounded resistor 53 and to e Condenser t4. Condenser 6,4 is conneetedby means. of a Conductor t5 to the plate 54 Whieh is .Connected through a plete leed resistor 66 tothe .source of plete current inverter 52. ieeds into e rectifier ti which consists of two rectier tubes 68 and 69 These tubes have cathodes 1D and 1Iy and plates 12 and 13. The plate 540i tube 53 is connected by means of the conductor 65 to a condenser Which in turn is connected by means of a con-A The aangaan ductor to the cathode 10 of tube 68. The plate 55 of tube 53 is connected by means of a conductor 16 to a condenser 11 which in turn is connected by means of a conductor 18 to the cathode 1| of tube 6.9. The two plates 12 and 13 are connected together and to a conductor 19 which is connected to a manually controlled double pole double throw switch 80. This switch has two sections 8| and 02. The section 8| has a movable contact 83 and xed contacts 84 and 85. The section 82 has a movable contact 86 and fixed contacts 81 and 88. The conductor 19 is connected to the movable contact 83 of section 8| of said switch. The conductor 19` is further connected to a condenser 4| and a resistor 36 which are connected in parallel and grounded. The contact 85 of switch 80 is connected by means of a conductor |80 to a limiter and slicer 89. This limiter and Slicer consists of a condenser 90, a resistor 9| and a rectifier tube 92, having a cathode 93 and a plate 94. The said limiter and slicer further includes a resistor 95 and a condenser 96 and still another resistor 91. Resistor 95 is connected by means of a conductor 98 with the condenser 96. This condenser is connected by means of a conductor S9 with the resistor 91 which is grounded. Conductor 98 is connected to another conductor |00 which is connected to the cathode 93 of tube 92 and to the condenser 90 and resistor 9| which are connected in parallel. This condenser and resistor are further connected to a conductor |0|. The plate 94 of tube 92 is connected to a source of direct current |02 which is connected by means of a conductor |03 to another source of direct current |04. This latter source of direct current is grounded. The conductor |0| is connected to the conductor |03. The limiter and slicer 89 is connected to an amplifier |05. This amplier consists of a thermionic pentode |06 including a plate |01, a suppressor grid |08, a screen grid |09, a control grid I I0 and a cathode Cathode is connected through a cathode resistor ||2 to ground which is bypassed by a condenser |84, while the control grid l0 is connected by means of a conductor ||3 to the conductor 99. The plate |01 is connected to a plate load resistor ||4 which is connected to a conductor ||5 which in turn is connected to a source of plate current.

The amplifier |05 is connected to a trigger pulse generator ||6. This generator includes a twin triode ||1 having two plates ||8 and H9, grids |20 and |2| and cathodes |22 and |23. The cathodes |22 and |23 are connected together and to a cathode resistor |24 which is grounded. The control grid |20 is connected by means of a conductor |25 through a coupling condenser |26 to the plate |01 of amplier tube |05. Grid bias is furnished for the grid |20 by means of a potentiometer |21 which is connected through a` conductor |28 to the source of plate current supply. This potentiometer is connected through a fixed resistor |29 with the conductor |25. Plate current is supplied to the plates IIB and ||9 through load resistors |30 and |3| which are connected by means of a conductor |32 to the source of plate current. The cathode |22 of tube ||1 is connected by means of a conductor |33 to a resistor |34 which is connected to the grid |2| of said tube. The said grid is further connected to a condenser |35 which is connected to the plate 8 by means of a conductor |36. This conductor is connected to a condenser |31 which in turn is` connected to a resistor |38.y

This resistor is connected by means of a conductor |39 with the movable contact 86 of switch section 82 of switch 80. A condenser |40 and a resistor |4| are connected to the conductor |39 and to ground. The xed contact 88 of switch section 82 is connected by means of a conductor |42 with the xed switch contact 84 of switch section 8| which in turn is connected by means of a conductor |43 with a switching stage |44.

The switching stage |44 includes a converter tube |45 having a plate |46, a suppressor grid |41, a screen grid |48, a cut-01T grid |159, a control grid |49 and a cathode |50. The cathode |50 is grounded through a bias resistor |13 which is bi-passed by a condenser |14. The control grid |49 of this tube is connected by means of a conductor |5| to a tap |52 on the conductor 38 of the transmission line 31. 'Ihis tap divides the transmission lines 31 into two parts, the one part being designated by the reference numeral |53 and forming a second shorting line and being that part nearest the shorted end of the said transmission line. The said tap further forms another part in said line adjacent the input end of the line and which forms a signal delay line indicated by the reference numeral |54. The plate |46 of the tube |45 is connected by means of a conductor |55 with the primary |56 of a push pull transformer |51. This primary has a center tap |58 which is connected to a suitable source of plate current. The cut-off grid |59 is connected to the conductor |43 by means of a conductor |60. The secondary |6| is provided with a center tap |62 which is connected to a screen |63 between the said primary and secondary and which is grounded. The ends of the said secondary are connected together and to a conductor |64 which is adapted to be connected to the antenna terminal of the receiver. By means of this construction the secondary |6| is divided into two sections `|11 and |18 which are wound in opposite directions and which are connected in parallel across the conductor |64 and the screen |63.

The switching stage |44 further includes a balancing tube |65 which is identical with the tube |45. This tube has a plate |66, a suppressor grid |61, a screen grid |68, aout-off grid |69, a control grid |10 and a cathode |1|. The cathode |1| is grounded through a bias resistor |15 which is by-passed by a condenser |16, while the control grid |10 is connected through a dummy resistor |12 to ground. The cut-olf grid |69 is connected by means of a conductor |19 to the conductor |43.

The operation of the invention is as follows: For the purpose of describing the operation of the invention it will be assumed that an eX- ponental pulse has been superimposed on the carrier signal frequency andhas been received by the antenna. An oscillogram showing a wave representing the potential of the combined pulse and carrier wave whichis indicated by the reference character A is shown in Fig. 2. is prevented from reflecting back and forth on the antenna and lengthening itself by the antenna being terminated in resistor l2 which has a resistance value equal to the characteristic impedance of the antenna. The tube I3 transfers this potential shown in Fig. 2 to the first shortening line 23. This first shortening lineV reilects this wave of Fig. 2 from the shorted end` once andfurther reflections are prevented by the input vend of the line being terminated in the :resistor 24 having a. .resistance `in seminarios The `wave 4 egcs-desa 7 with resistor 32 in parallel with it equal tothe characteristic impedance of the rst shortening line 23. rIhe resultant potential at the grid of tube 3| is then as shown in Fig. 3, vand is represented by the lobe "B, The lengthof the line 31 is such that the desired signal is not materially reduced. A signal for which the electrical line length isa quarter wave length will by the reection be increased by a factor of two. A signal for which the length is a half wave length will be cancelled. Most of the region of the signal between those two will be transmitted in useable fashion by the line with voptimum.energy transfer in a wide bandwidth about the rst frequency for which the line is a Vquarter wave length, On the other hand, for a `static pulse which is of long duration the reflection essentially climi@ natos all but' the first portion of length equal to twice the electrical length of the transmission line. However, because many static pulses are rectangular in shape as the above mentioned long pulse and also because of the attenuating effect of transmission lines producing a slightly smaller canceling reflection than the original pulse which results in 'a residue potential after the first shortened section, it is necessary to utilize at least one more shortening line. For this purpose the shortening line |53, being a part of the cancellation line 31, is employed to reduce the initial wave shown in Fig. 2 to that showing the shortened pulse C in Fig. 4 which has two lobes D and E. This shortened pulse would still cause considerable interference applied directly to the receiver so it is essentially blankedV by passing through the switching stage tube |45 which is biased to cut off during the time this shortenedimpulse isVV present by means of a controlled blanking pulse derived from the original static pulse shown in Fig. 2. The delay line |54 forming a part of the cancellation line 31 provides a time delay for passing the signal to the switching stage in order that there will be sufficient time for the static pulse t be detectedand formed into a nal blanking pulse arriving at the switching stage vjust prior to and overlapping thetime interval in which the shortened static pulse C of Fig. 4 is arriving at tube |45. The potential at the input end of the cancella.- tion line 31 diifersefrom that shown in Fig. l by having a separation between the. two lobes D and E equal to twice the electrical length of the cancellation line 31 as shown in Fig, 5 which in turn is applied through tube. 4.3 to the reflecting line 4B. This reflecting line is essentially open circuited at the input end and short cire cuited at its outer end so that the pulses reflect back and forth.` The lobe D of Fig. 5 thus reflects back and forth until further reflections are cancelled by the incoming pulse produced by the cancellation line, thus producing a definite number of pulses F as shown in Fig. 6. lIhe cancella-- tion line length is an even numbered multiple of the reflecting line, length which in turn is equal in length to the length of the first shortening line 2.3.. The multiple number determines the number of pulses I. Fie. 6- These pulses of Fig.V 6. are; in turn applied tothe inverter 52 which amplies and inverts the positive llobes G of the pulses C to provide full wave rectification through the rectifier tubes 68 and 6.9' resulting in the negative pulse I-I of Fig. 7. The condenser 4| and resistor 3E combination have such time constants as do not appreciably broaden the pulse produced by the inverter 5 2 and rectifier- BT, thus` producing the pulse H of Fig. 7. This 8 pulse I have termeda blanking'pulse as it may be used to go directly to the switching stage |44 to cut -oi tube |45 as previously stated. When the switch 8|) is in its upper position this blanking pulse would be so used which is desirable-whe'n the nature of the static pulses arriving `a-re ef high level, large in number, and relatively uniform, because in such case as many as 500,000 static pulses may be blanked out per second which is many times greater than is possible withother noise limiters commonly used within the receiver and functioning after the receiver circuits have been set into shock 'excitation. To prevent the cut off of switching tube |45 from producing noise by virtue of ces- Y Since the switching stage operates at micro-volt levels, ahead of the receiver tuned circuits it is essential that very careful balancing be accom.- plished in this stage to prevent switching noise. The output transformer |51 must be carefully balanced and to accomplish transfer from push pull to single ended feed to the receiver the out.- put transformer secondary is constructed with two win-dings which are arranged to produce opposing voltages and are connected in parallel so that the mid point may be grounded and complete electrical balance is maintained. An elec trostatic shield is provided between the windings to prevent electrostatic energy transfer in the switching stage. The resulting potential after theV switching stage has functioned and directed to the receiver is shown in Fig. l0. In the case where the static pulses are sporadic and widely varying in voltage amplitudes the blanking pulse H of Fig. 7 would also vary and produce erratic operation of the switching stage for lower level static pulses. Therefore, in such case the switch would be moved to its lower position whereby the slicer and limiter 89 would become effective which shapes and limits the pulse I-I o f Fig. 'i by forming a uniform trigger pulse I which is shown Yin Fig. 8. This trigger pulse is amplified by amplifier |05. and modified by the trigger pulse generator ||6 resulting in the formed pulse J shown in Fig. 9.

The advantages of the. invention are manifest. The apparatus operates before the signal is. receivedA at the receiver tuning circuits thereby preventing amrllcation of thev static pulse within the receiver by shock excitation. This allows a very large number of pulses to be blanked out without. interfering with the desired signal. With the instant invention reconstruction andgalteration of. the receiver need not be made- Y The Gircu elements which detect and form the blanking pulse are forthe most part separate from the signal generator and thus do not modify the signal. With this invention more perfect elimination of noises can be procured than where the noise is merely reduced in volume within the receiver. For instance, wave corona pulses may be removed froml an antenna, when an airplane is flying in precipitation static or thunder storm conditions causing various parts of the airplaneto go into corona, producing pulse reifietiticn of the' order of 100,000 per second. Noise limiter-s Normal signal plate variations practically all the time on the shock excitation broadened pulses under such circumstances.

Changes in the specic form of the invention, as herein described, may be made within the scope of what is claimed without departing from the spirit of the invention.

Having described the invention, what is claimed as new and desired to be protected by Letters Patent is:

l. In apparatus for static pulse rejection for radio receivers, an antenna, energy transferring means coupled to the antenna and to the receiver and including a switch connected to the antenna ircuit of the receiver and adapted upon actuation to disconnect the receiver from the antenna, a pulse shortening transmission line shorted at its outer end and terminated at its input end in an impedance substantially equal to itsicharacteristic impedance, a coupling device connected to said antenna and to said transmissionline at its input end, said energy transferring means being connected to said input end, said transmission line shortening long static pulses arriving at said transmission line, and control means coupled to the input end of said transmission line and coupled to said switch for operating said switch to blank out the static pulses prior to arrival at said receiver.

2. in apparatus for static pulse rejection for radio receivers, an antenna, energy transferring means coupled to the antenna and to the receiver and including a switch coupled to the antenna circuit of the receiver and adapted upon actuation to disconnect the receiver from the antenna, a pulse shortening transmission line of a length substantially equal to a quarter Wave length of the optimum signal frequency desired, said transmission line being shorted at its outer end and terminated at its input end in an impedance substantially equal to its characteristic impedance, a coupling device connected to said antenna and to said transmission line at its input end, said energy transferring means being connected to said input end, said transmission line shortening long static pulses arriving at said transmission line, and control means coupled to the input end of said transmission line and coupled to said switch for operating said switch to blank out the static pulses prior to arrival at said receiver.

3. In apparatus for static pulse rejection for radio receivers, an antenna, energy transferring means coupled to the antenna and to the receiver and including an electronic switch connected to the antenna circuit of the receiver and adapted upon actuation to disconnect the receiver from the antenna, a pulse shortening transmission line shorted at its outer end and terminated at its input end in an impedance substantially equal to its characteristic impedance, a coupling device connected to said antenna and to said transmission line at its input end, said energy transferring means being connected to said input end, said transmission line shortening long static pulses arriving at said transmission line, delay means, a coupling device connected to the delay means and to the transmission line, said delay means delaying the arrival of the shortened pulse at the receiver, a second transmission line of a length equal to an even numbered multiple of the length of the iirst transmission line, said delay means being a portion of said second transmission line, said second transmission `line being shorted at its outer end and terminated at its input end in an impedance substantially equal to its characteristic impedance, a coupling device connected tothe first named transmission line and to the input end of said second transmission line, said second transmission line forming from said shortened pulse two pulses of opposite polarity spaced in time from one another, a third transmission line of the same length as said irst transmission line, shorted at its outer end and effectively open circuited at its input end, a coupling device connected to said second transmission line and to the input end of said third transmission line, said third transmission line in conjunction with said second transmission line producing a deiinitely limited sequence of pulses of both polarities, rectifying means coupled to said third transmission line at its input end and rectifying said pulses to produce a single blanking pulse of predetermined time extent andpolarity and means for connecting the output portion of said rectifying means to said switch.

f1. In apparatus for static pulse rejection for radio receivers, an antenna, energy transferring means coupled tothe antenna and to the receiver and including a switch connected to the antenna circuit of the receiver and adapted upon actuation to disconnect the receiver from the antenna, a pulseshortening transmission line of a length substantially equal to an odd number of quarter wave lengths of the optimum signal frequency desired, said transmission line being shorted at its outer end and terminated at its input end in an impedance substantially equal to its characteristic impedance, a coupling device connected to said antenna and to said transmission line at its input end, said transmission line shortening long static pulses arriving at said transmission line, and control means connected to the input end of said transmission line and to said switch and operating said switch to blank out the static pulses prior to arrival at said receiver.

5. In apparatus for static pulse rejection for radio receivers, an antenna, a resistor effectively equal to the surge impedance of the antenna and terminating said antenna, energy transferring means coupled to the antenna and to the receiver and including a switch connected to the antenna circuit of the receiver and adapted upon actuation to disconnect the receiver from the antenna, a pulse shortening transmission line shorted at its outer end and terminated at its input end in an impedance substantially equal to its characteristic impedance, a coupling device connected to said antenna and to said transmission lineat its input end, said Vtransmission line shortening long static pulses arriving at said transmission line and control means connected to the input end of said transmission line and to said switch and operating said switch to blank out the static pulses prior to arrival at said receiver.

6. In apparatus for static pulse rejection for radio receivers, an antenna, energy transferring means coupled to the antenna and to the receiver and including a switch connected to the antenna circuit of the receiver and adapted upon actuation to disconnect the receiver from the antenna, a pulse shortening transmission line shorted at its outer end and terminated at its input end in an impedance substantially equal to its characteristic impedance, coupling means connected to the lantenna and to said transmission line at its input end, said transmission line shortening long static pulses arriving at said energy transferring means, a second coupling means, modifying means including reecting means connectedA to the input end of.- said transmission line through said second coupling.meansfandfforming .a prei vdetermined .number of reilected pulsesA from `the shortened pulse produced by, said transmission line, a rectiiier coupledrto said modifyingmeans and forming a blanking pulse: of predetermined polarity from said reiiected. pulses, and` means including said rectifier connected tosaid modifying means and -tosaidswitch forfoperating said switch from said bla-hiring, pulse.

7. In apparatusvfor static pulse rejection for radio receivers, an antenna,l energyftransferring means coupled to thel antenna and to the receiver and including a switch :connectedto the yantenna circuit of the receiverandiadapted` upon actuaE tion to disconnect the receiver from Vthe-antenna, a pulse shortening transmission line 'shorted at its outer end and terminated at itsvinput endin an impedance substantially,f equal to -its characf teristic impedance, couplingmeansconnected, to the antennaandto sad/transmissioniline at 4its, inputvuend,v said transmission line shortening long static pulses arrivingv atsaid energy transferring means to yform shortened pulses, a-vsecondfcouf pling means, cancellationY means connected, to the-input end ofsaiditransmission line through said second couplingL means,- said cancellation means being shorted'atits-outer endend-iter minatedat its input end-in animpedancesub ,stantially equal toits characteristic impedance, a lthird Vvcoupling, lmeans connected to. the input endofsaid cancellation means,reecting means connected tor the. output-of -said thirdcoupling means, said cancellation .means and said reflecting. means cooperatively functioning to form a plurality of reflected pulses from said shortened pulsesv and to simultaneously limit the number of said reiiected pulses, arectier coupled to said reflecting mea-ns and formingv a-blanking pulse of predetermined polarity from said reflected pulses, and means connected to said blanking means and. to. said switch for operating said switch from saidblankng. pulse.

MORRIS M. NEWMAN.

ReferencesvCited in the le of this patent UNITEDSSTA'IES PATENTS- Number Name Date 2,151,145; Percival' Mar. 21, 1939 2,151,739: Burrll'- Mar. 28, 1939 2,151,774 Koch Mar. 28, 1939 2,225,524- Percival Dec. 17, 1940 2,236,134 Gloess Mar. 25, 1941 2,450,352 Piety Sept. 28, 1948 2,531,164 Sands-etal Nov. 21, 1950 FOREIGN PATENTS Number Country; Date 442,626.` Great Britain- Feb. 12, 1936 

